Disc drives are used to record and reproduce information stored on recording "media" or discs. Conventional disc drives employ a plurality of vertically-arrayed discs, each disc having a top and bottom surface with a magnetic coating for storing data. The discs are spaced from one another by a distance sufficient to allow magnetic read/write heads to pass over both the top and bottom surfaces of adjacent discs.
The vertical array or "stack" of discs are typically journaled about the cylindrical hub of a spindle motor which is mounted on a fixed shaft for high speed rotation within the disc drive housing. The disc stack includes a bottom disc supported by a lower flange of the spindle motor hub. A series of additional discs and spacer rings are then stacked on top of the bottom disc in an alternating pattern. Once the disc stack and spindle motor have been assembled into a "disc pack," a clamp ring is fitted over both the top of the spindle motor hub and the top disc of the disc stack to secure the discs and the spacer rings to the hub. Following assembly, the disc pack is spin balanced and counterweights are applied as necessary to reduce any wobble or run-out due to imbalance or an offset center of gravity. In light of recent increases in track density on current generations of disc drives, even small degrees of disc wobble can lead to tracking errors.
Thus, each disc pack is typically required to pass a number of diagnostic and spin balancing tests before installation within a disc drive. However, if the disc pack fails any of the tests, it is typically sent for "reworking." For example, if a diagnostic shows that one or more of the discs are defective, the entire disc pack must be reworked to replace the defective disc. Likewise, reworking is required if the spindle motor is found to be defective or if the imbalance of the disc pack is too large to be cured by counter eights. It is common for approximately 10-15% of disc packs on a production line to require reworking.
Reworking a disc pack requires that each of the discs and the spacer rings be removed one at a time and stacked in inverse order on a rack. Even if only one of the discs is found to be defective (e.g., the second disc from the top of the stack), it is typically required that all of the discs and spacer rings be removed and then restacked on the spindle motor hub to ensure that the discs are properly centered and balanced after reworking. Indeed, a shim is typically applied to the empty motor hub prior to restacking the discs to aid in centering the discs and spacer rings about the motor hub, thereby maintaining the concentricity of the discs and reducing run-out errors. However, the process of manually transferring each disc and spacer ring from the spindle motor to a stand, and then transferring all of the discs and spacer rings back to the spindle motor requires a great deal of time and operator skill to prevent damaging the fragile discs during the reworking process. However, even with skilled operators, the manual handling of each disc within the disc pack will inevitably damage a number of discs. Furthermore, although the disc drive assembly line is located within a clean room facility, the time-consuming rework process increases the chances that the discs will be exposed to contaminants that will adversely affect the performance of the disc drive.
It is with respect to these and other background considerations, limitations and problems that the present invention has evolved.